1. Field of the Invention
The present invention relates to a neutral point voltage adjuster in a torque sensor which uses a neutral point as a boundary of right and left directions, and detects each torsional torque in the right and left directions on the basis of an inductance change in a pair of coils.
2. Description of the Related Art
In a torque sensor, unless an output voltage (a neutral paint voltage) at a neutral point which no torque is inputted, is outputted as a predetermined voltage, control is not accurately carried out.
So, the following methods have been proposed; more specifically, there is a method of setting the output voltage of the torque sensor to a predetermined reference voltage by operating a manually variable resistor, and a method of previously measuring an error between the output voltage of the torque sensor and the predetermined reference voltage, and compensating and controlling the error when carrying out control.
However, according to the former method, that is, a neutral point voltage adjusting method by a variable resistor, fluctuation of resistance valve is common, reliability is low, and further, adjusting operation is troublesome.
According to the latter method, that is, a method of correcting an error when carrying out control, the output of the torque sensor contains an error; for this reason, a control side must recognize an error peculiar to the torque sensor, and therefore, this method is not in general use.
The present invention has been achieved in view of the above problem. It is, therefore, an object of the present invention to provide a neutral point voltage adjuster of a torque sensor which can simply and securely adjust a neutral point voltage, and is excellent in general use.
To achieve the above object, the present invention provides a neutral point voltage adjuster of a torque sensor which comprises: a pair of coils having inductances changing mutually in a reverse direction in accordance with a torque; and a differential amplifier means inputting first and second sub-voltages based on each inductance change of both coils, and amplifying a difference between the first and second sub-voltages so as to output it as a main voltage, and which uses a neutral point where no torque is inputted as a boundary between right and left directions, and detects each torsional torque in the right and left direction. A neutral point voltage setting means is employed for displacing a main voltage of an output from the differential amplifier means on the basis of an adjusting signal so as to set a neutral point voltage; a staring means for staring a neutral point voltage setting state by the neutral point voltage setting means; and a neutral point voltage adjusting means for storing a neutral point voltage used as a reference of a main voltage, and inputting the main voltage, and further, outputting the adjusting signal to the neutral point voltage setting means so that a difference between the neutral point voltage read from the main voltage and the reference neutral point voltage is made small.